Prior to the onset of the hiccups, was your daughter under a lot of stress? You might want to check into the possibility of a magnesium deficiency. Most american kids get plenty of calcium, but not magnesium. Too much calcium blocks magnesium absorption. Some symptoms of magnesium deficiency are muscle cramps, (hiccups are muscle spasms of the diaphragm,) muscle spasms of the face, (tics)tingling, numbness, anxiety, stress, and insommnia. There are many more.
I give my 16 year old daughter, daily, a 1/2 tsp of magnesium citrate(310 mg) - it is a powder that dissolves in juice.
I also agree with some of the other suggestions about taking her to a chiropractor - especially one that specializes in children.
You want to discover and treat the cause, not the symptom. Good luck.